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Tuesday, August 23, 2005 |
...TROPICAL STORM WATCH ISSUED FOR PORTIONS OF THE FLORIDA KEYS AND FLORIDA EAST COAST... At 11 PM EDT, the center of Tropical Depression Twelve was at 23.4 North 76.0 West, 140 miles southeast of Nassau, Bahamas and moving to the northwest at 7 mph. Maximum sustained winds are 35 mph and minimum central pressure is 1007 millibars (29.74"). Last observations from recon and current surface observations justify holding the intensity at 35 mph. However, there are indications that intensifcation is occurring now such that the depression would become a tropical storm in the next several hours. The depression is currently in an area of weak steering currents, hence its slow motion. This motion is expected to persist through the forecast period with a bend to the west in 36 hours or so. This is the forecast offered by most of the global forecast models, with the exception of the GFS model, which more or less stalls the system over Florida. Given the apparent organization trend, the depression could become a tropical storm by morning. Beyond that, there is much uncertainty. Intensity guidance is widely split, with one model not bringing the storm above tropical storm strength, and another insisting on a hurricane by time of landfall. The official forecast continues to be on the conservative side and brings a strong tropical storm ashore. A tropical storm warning could be issued tomorrow for areas currently under the tropical storm watch. If intensification goes beyond what is currently forecast, a hurricane watch could be issued. Forecast is highly uncertain, and that is reflected in an experimental forecast product, which shows equal probabilities of tropical storm force winds throughout the watch area (rather than being concentrated or centered on a particular area). Well, a fair amount of the uncertainty from earlier is gone now. It appears that the multiple centers of circulation are consolidating, which certainly helps the forecast as it narrows the possibilities. The downside to this consolidation is that does represent a significant improvement in organization, a necessary step for further intensification. With conditions at they are at the moment, poor organization was the only inhibiting factor in the near term. The storm may manage to get a fair bit in ahead of the National Hurricane Center's intensity forecast, although unfavorable upper-air conditions over Florida may be enough to keep it in check as it approaches the coast. Nonetheless, residents of south Florida should be prepared for high winds (60-80 mph) on Friday. Uncertainty in the later forecast period will be reduced tomorrow evening when the Gulfstream-IV goes on its upper-air 'surveillance' mission. The data collected should help resolve the questions over the orientation and strength of the mid-upper level ridge of high pressure that will be key to the future movement of the storm. Elsewhere in the tropics, the tropical wave west of the Cape Verdes Islands looked a little bit better on satellite tonight as it heads out of an area of unfavorable wind shear. Dry air, however, continues to inhibit its progression towards a tropical depression. 2005 Hurricane Season, Weather comment []11:42:43 PM  trackback []
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| At 5 PM EDT, the center of newly formed Tropical Depression Twelve was at 23.2 North 75.5 West, 175 miles southeast of Nassau Bahamas and moving to the northwest at 8 mph. Maximum sustained winds are 35 mph and minimum central pressure is 1007 millibars (29.74"). The government of Bahamas has issued Tropical Storm Warnings for the central and northwest islands and a tropical storm or hurricane watch is possible for south Florida later this evening. Data from the reconnaisance plane as well as surface observations indicate that the area of low pressure over the Bahamas is sufficiently organized to warrant classification as a tropical depression. Estimate of inital motion is to the northwest at 8 mph. The low level center is in a state of flux, and as such its exact position is uncertain. However, there is a broad low level circulation. The depression is forecast to move north through a gap in the high pressure ridge that exists over the southeast U.S. All of the global models fill in that gap, which cause their forecasts to feature a turn to the west , bringing the storm across south Florida in 72 hours and into the Gulf of Mexico in 96 hours. The intensity forecast is challenging due to the uncertainty on how and when the storm will feature a well defined center. All factors are favorable for intensification and provided that the storm becomes organized within the next 24 hours, it would be a hurricane by the time it reached the coast. The official forecast keeps it just under hurricane strength as it crosses Florida, which is slightly more conservative than their model guidance. Because a well defined feature from Tropical Depression Ten did not persist in a clear manner, NHC decided to classify this as a new storm. This differs from the case of Ivan last year, in which a feature clearly remained from the time it originally made landfall to the time it reentered the Gulf of Mexico and was classified a tropical storm once again. A very challenging forecast due to the uncertainty over exactly where a dominant center of circulation will form at. Here is the model guidance that NHC had to work with. The most reliable of the forecasts shown in the graphic is the one labled 'CONU', which is a consensus of particular dynamic models that produced a forecast. Residents of south Florida will certainly want to keep a close eye on this, because if it were to become become organized, it could intensify fairly quickly (but not so much that it would be a dire threat). For most people, preparation will be limited to bringing inside stuff like lawn furniture that could get strewn about by 65-75 mph winds. Boat owners will want to be mindful of the possibility of hurricane warnings being posted on Wednesday night or Thursday if the storm becomes better organized. There is far too much uncertainty tpresent for me to have much confidence in any comments beyond that. People along the gulf coast from Pensacola to the Texas border may need to start paying attention to this system after this weekend, but that is not necessarily a guarantee at this time.
2005 Hurricane Season, Weather comment []5:41:17 PM trackback []
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| Tropical Storm Jose went ashore last night and is now dissipating over Mexico. The Hurricane Hunters are in the air on their way to investigate the system that is currently located between the Bahamas and Cuba. If sufficient organization is found, the system will be declared a tropical depression (and probably will receive a new number as I stated yesterday). Elsewhere, the tropical wave west of the Cape Verdes Islands continues to persevere in a somewhat unfavorable enviroment. Nevertheless, tropical depression formation is possible within the next two days. Source: National Hurricane Center's Tropical Weather Outlook 2005 Hurricane Season, Weather comment []11:21:37 AM trackback []
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Last update: 9/15/2005; 9:46:05 AM .
